Pressure ulcers, injuries to the skin and underlying tissues caused by prolonged pressure on the skin, are among the most common and costly secondary conditions after spinal cord injury (SCI). Pressure ulcers affect about 80% of individuals with SCI, with 30% of SCI patients developing multiple pressure ulcers. The annual cost of care is about $1.2 billion in the USA. In particular, the annual incidence rate ranges from 20-31% of SCI patients, and cost of care is estimated to be $40,000 per occurrence.
To aid in the prevention of pressure ulcers, pressure relief activities every 15-30 minutes have been recommended for persons with SCI. To minimize harmful pressure from sitting in a wheelchair, air-filled cushions are widely used by persons with SCI. Even if the person performs regular pressure relief activities, these cushions are typically ineffective in preventing ulcers if the cushions are over- or under-inflated. This is because people with SCI typically lack the sensation to detect when and where the cushion is “bottoming-out.”
A number of different monitoring solutions have been attempted to address this issue, but they all suffer from shortcomings. Pressure-mapping systems measure the distribution of pressure on the interface between the cushion and the body. However, the high price (e.g., thousands of dollars) make such systems infeasible for widespread use. Currently used air pressure monitors are ineffective because air pressure changes with the applied load and does not reflect changes in weight distribution.
In addition, the SCI population is also at 2.5 times higher risk of obesity and overweight then those without the disability. Moreover, individuals who use a wheelchair have greater difficulty maintaining healthy weight because they have fundamental challenges in estimating physical activity and body weight. More strikingly, given the same BMI, persons with SCI usually carry a larger amount of fat than those without disabling conditions. Acutely, persons with SCI tend to lose weight because of the catastrophic injury and related hypermetabolism. After the acute phase, however, resting energy expenditure decreases with the loss of metabolically active muscle mass, and activity energy expenditure also decreases with a sedentary lifestyle. Without an appropriate dietary adjustment, energy intake can easily exceed daily energy requirements, leading to a weight gain. Maintaining healthy weight is complicated by the challenges in estimating physical activity and body weight in individuals who use a wheelchair. Physical activity monitoring solutions may range from wrist-worn accelerometers and multi-sensor body-worn systems to wheelchair-mounted systems. All body-worn sensors present an additional burden to the wearer and thus are not well suited for long-term use. Wheelchair-mounted device so far have been limited to tracking mobility of manually-propelled chairs rather than activity of the occupant. Similarly, attempts have been made to incorporate weight measurement capabilities into the wheelchair. However, such devices require physical modification of the wheelchair. Therefore, non-intrusive and accurate monitoring of physical activity and body weight of wheelchair users remains an open problem.
Therefore, a cost-effective monitoring program is needed to alleviate the burdens facing SCI survivors.